Communication devices, method for detecting an edge in a received signal and method for receiving data

ABSTRACT

A communication device includes a receiver configured to receive a signal, a sampler configured to sample the signal for each digital value of the predefined sequence of digital values in the signal, a memory configured to store a table giving, for each of a plurality of combinations of one or more preceding first digital values and a following second digital value, a threshold for a signal level to detect the second digital value, an initializer configured to, for a combination in a subset of the plurality of combinations, initialize the table based on a sample of the signal for the second value, and for a combination outside of the subset, select a combination from the subset and initialize the table based on a sample of the signal for the second value of the selected combination.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/602,199, filed May 23, 2017, and incorporated herein by reference inits entirety, which claims priority to German Patent Application SerialNo. 10 2016 109 799.3, filed May 27, 2016, and incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to communication devices, methods fordetecting an edge in a received signal and methods for receiving data.

BACKGROUND

Wireless communication such as radio communication between a chip cardreader and a chip card may be based on a protocol such as ISO 14443which has asynchronous timing and lacks synchronization and trainingpatterns. For using a synchronous digital receiver in such a scenario,approaches which nevertheless allow efficient synchronization andtraining are therefore desirable.

SUMMARY

A communication device is provided including a sampler configured tosample an input signal, wherein the sampler is configured to generate asampled value for each sampling time of a sequence of sampling times, asequence value generator configured to generate an output value for eachsampling time of the sequence of sampling times based on the sampledvalues, wherein the sequence value generator is configured to set theoutput value for a sampling time based on the sampled value for thesampling time and based on a limitation of the difference between theoutput value for the sampling time and the output value for thepreceding sampling time in the sequence of sampling times and an edgedetector configured to detect an edge in the input signal based on theoutput values.

Further, a method for detecting an edge in a received signal accordingto the communication device described above is provided.

Further, a communication device is provided including a receiverconfigured to receive a signal representing a predefined sequence ofdigital values from a transmitter, a sampler configured to sample thesignal for each digital value of the predefined sequence of digitalvalues, a memory configured to store a table giving, for each of aplurality of combinations of one or more preceding first digital valuesand a following second digital value, a threshold for a signal level todetect the second digital value, wherein the predefined sequence ofdigital values represented by the received signal includes a subset ofthe plurality of combinations, an initializer configured to for acombination in the subset of the plurality of combinations, initializethe table based on a sample of the signal for the second value and for acombination outside of the subset, select a combination from the subsetand initialize the table based on a sample of the signal for the secondvalue of the selected combination and a data recovery circuit configuredto receive data from the transmitter based on the initialized table.

Further, a method for receiving a signal according to the communicationdevice described above is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments of the invention are described with reference to thefollowing drawings, in which:

FIG. 1 shows a communication arrangement including a reader and a chipcard;

FIG. 2 shows a communication arrangement including a reader and an ASK(amplitude shift keying) digital receiver;

FIG. 3 gives an example of the structure of a data recovery module;

FIG. 4 illustrates the direct sampling of a digitalized envelope;

FIG. 5 shows a symbol synchronizer according to an embodiment;

FIG. 6 shows an example of the operation of the symbol synchronizer ofFIG. 5;

FIG. 7 shows a diagram illustrating an example of symbolsynchronization;

FIG. 8 shows the architecture of a data recovery module according to anembodiment;

FIG. 9 illustrates a training procedure;

FIG. 10 shows an ASK receiver based on the synchronisation describedwith reference to FIG. 5 and the data recovery described with referenceto FIG. 6;

FIG. 11 shows an example for an implementation of a differentiator;

FIG. 12 shows a communication device according to an embodiment;

FIG. 13 shows a flow diagram illustrating a method for detecting an edgein a received signal;

FIG. 14 shows a communication device according to a further embodiment;and

FIG. 15 shows a flow diagram illustrating a method for receiving data.

DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and aspects of thisdisclosure in which the invention may be practiced. Other aspects may beutilized and structural, logical, and electrical changes may be madewithout departing from the scope of the invention. The various aspectsof this disclosure are not necessarily mutually exclusive, as someaspects of this disclosure can be combined with one or more otheraspects of this disclosure to form new aspects.

FIG. 1 shows a communication arrangement 100 including a reader 101 anda chip card 102. The reader includes an antenna 103 which is for examplearranged in a housing onto which the chip card 102 is placed. The chipcard 102 includes a chip card module 104 and a chip card antenna 105.

The reader 101 and the chip card module 104 may communicate by means ofthe antennas 103, 105.

A contactless chipcard (or generally a contactless transponder)according to ISO 14443 communicates with a reader using amplitude shiftkeying (ASK) modulation. Two different modulation indexes are defined:10% (nominal) for the so called Type-B communication and 100% for Type-Acommunication.

In the following embodiments a receiver circuit (e.g. used in chip cardmodule 104) for a ISO 14443 Type-B transponder is described, addressingthe basic frame type where the asynchronous timing (SOF(start offrame)-high, SOF-low, EGT (extra guard time) between two bytes, EOF(endof frame)) and the lack of synchronization and training patterns do notallow to employ algorithms for an ASK synchronous receiver.

FIG. 2 shows a communication arrangement 200 including a reader 201(e.g. corresponding to the reader 101) and an ASK digital receiver 202(e.g. corresponding to the chip card module 104).

The reader 201 includes a reader antenna 203 via which it sends an(ASK-) modulated radio signal to the receiver 202. The receiver includesa resonance circuit 204 (including an antenna 205 and a capacity 206 inparallel to the antenna 205) which receives the modulated radio signalas a modulated input signal. The modulated input signal is rectified bymeans of a rectifier 207 and its analog envelope is extracted by meansof a peak detector 208. The digital envelope is digitalized by means ofa analog-to-digital converter 209 and a data recovery module 210extracts the transmitted data based on a data recovery algorithm.

It should be noted that since the reader steadily transmits the carriersignal, the receiver can recover the clock timing in a straightforwardmanner.

FIG. 3 gives an example of the structure of a data recovery module 300.

The data recovery module 300 for example corresponds to the datarecovery module 210.

The data recovery module 300 processes the digital envelope of themodulated input signal by means of a digital bandpass filter 301 inorder to detect the edges in the modulated input signal by a first edgedetector 302. The first edge detector 302 uses two thresholds to detectthe falling and raising edge, respectively. In general, the thresholdsmay be different and not constant but they can be adapted to the inputsignal, e.g. may be increased for faster (i.e. steeper) edges in orderto increase the robustness against overshoots or undershoots in themodulated input signal.

After this first edge detection by the first edge detector 302, the datatransmitted are available as a binary signal which is stillasynchronous. A second edge detection by a second edge detector 303(using a faster clock, e.g. 4 times the bit rate) is performed to detectthe beginning of each frame, i.e. the SOF (start of frame), and eachstart bit (since the bytes can be transmitted asynchronously). Thesynchronism extracted in this way is used by a sampler 304 to sample thebinary signal at the bit rate thus generating a serial stream ofreceived bits.

However, in the approach described with reference to FIG. 3,Inter-symbol interference (ISI) at high baud rates (especially in lowfield, tuned, where the quality factor of the input resonance circuit204 increases), causes a data-dependent variation of the edge slopes.This typically results in a variation of the band pass filter 301 outputand, in turn, of the binary signal output by the first edge detector302, i.e. after the threshold comparison. Further, the adaptivethresholds (used to handle overshoots and undershoots) cause additionaljitter. Additionally, the edge detection on the binary signal by thesecond edge detector 303 introduces a further jitter equal to the clockused for the detection (e.g. 4 times the bit rate). If the total jitterexceeds half the bit length, the sampler 304 is not able to extract thedata bit correctly.

In view of the above, instead of detecting the edges in the inputenvelope and then sampling the obtained signal in order to extract thedata as in the approach of FIG. 3, the digitalized envelope is,according to various embodiments, directly sampled.

FIG. 4 illustrates the direct sampling of the digitalized envelope.

A first diagram 401 shows a first example of the input signal 403 withsteeper edges and a second diagram 402 shows a second example of theinput signal 404 with flatter edges. Time increases from left to rightin both diagrams 401, 402.

Specifically, the edge rising time t_(r) and the edge falling time t_(f)are smaller than the reciprocal of the bit rate B_(r) for the firstexample 403, i.e. t_(r),t_(f)<1/B_(r), while they are higher than thereciprocal of the bit rate B_(r) for the second example 404, i.e. t_(r),t_(f)>1/B_(r).

It is desirable to find an optimal detection threshold, i.e. how todecide if a sample represents a logic 1 or a logic 0.

If t_(r)/t_(f)<B_(r) as in the first diagram 401, a threshold 405 set to(MAX+MIN)/2 is the optimal choice, where MAX and MIN are themaximum/minimum data values in the envelope. For the caset_(r)/t_(f)>B_(r) of the second diagram 402, the optimal threshold 406is not constant and depends on the previously received bits.

Further, symbol synchronization should typically be taken into account,i.e. to sample the envelope in order to achieve a low error probability.

Since no synchronization pattern is available at the beginning of aframe (except if the ISO14443 advanced frame options are used) thesynchronization is, according to one embodiment, performed by exploitinga single edge, every time a new synchronization is needed (e.g. at aSOF-low, a SOF-high, or a START-BIT). The symbol synchronization isdescribed in the following.

FIG. 5 shows a symbol synchronizer 500 according to an embodiment, e.g.arranged in the data recovery module 210 at its input, i.e. receivingthe digital envelope of the modulated input signal.

The digitalized envelope is first processed by an optional low-passfilter 501 (e.g. an average over 4 samples) to decrease the quantizationnoise and afterwards it goes through a slew rate limiter filter 502operating according toy[i]=y[i−1]+sign{x[i]−y[i−1]}×min{s,|x[i]−y[i−1]|}  (1)

where x[i] is the ith input sample of the slew rate limiter, y[i] is theith output sample of the slew rate limiter and s is the maximum slope towhich the signal is limited by the slew rate limiter 502.

Assuming a use of a clock for the synchronization circuit with a clockfrequency of f_(SAMPLE)=8×B_(r), if the slope s is set to (2^(n)×2m/(1+m))/8, where n is the number of input samples and m is the minimummodulation index to be supported, after the slew rate limiter, theoutput y[i] is independent from modulation index and falling edge timingof the input signal x[i].

A differentiator 503 looking at the difference between two y[i] samplesat distance n_(diff) generates a synchronization signal. For instance,if the synchronization point is to be set at the 5th clock cycle afterthe falling edge, the differentiator 503 compares the slew rate limiteroutput (i.e. the amount of change in the output of the slew rate limiterafter the 5th clock cycle) with a threshold of 5 s.

FIG. 6 shows an example of the operation of the symbol synchronizer fora low start bit of an input signal with minimum modulation index 601 andan input signal with a higher modulation index 602.

The slew rate limiter 502 generates an output signal 603 which is thesame for both input signals 601, 602, i.e. which is independent from themodulation index. The differentiator sets a synchronization pulse at thefifth sampling time (of f_(SAMPLE)) after the beginning of the fallingedge based on that at the fifth sampling time y[i] has fallen by athreshold of thr_(diff)≤n_(diff)*s=5 s.

Once synchronization with the input signal has been achieved on thereceiver side, the receiver can sample the bits of the digitalizedenvelope of the input signal at the bit rate frequency.

Due to the asynchronous timings in the protocol according to ISO 14443,re-synchronizations are performed according to one embodiment asillustrated in FIG. 7.

FIG. 7 shows a diagram 700 illustrating an example of symbolsynchronization for an input signal 710.

The receiver activates the synchronizer 500 at the beginning of thereception, in order to detect the start of a frame, indicated by thefalling edge of the SOF-low as described with reference to FIG. 6.Afterwards, the receiver can synchronously sample 9 etus (elementarytime units), which are low according to the protocol.

At the ninth sample, the receiver again activates the synchronizer 500changing the sign of the slope and the differential threshold) to detectthe SOF-high begin, i.e. the rising edge of the following SOF-high 702.After this second synchronization, the receiver can sample two etussynchronously which are high according to the protocol.

Finally, the receiver activates the synchronizer 500 to detect eachSTART-BIT begin, i.e. the falling edge of a START-BIT. Afterwards, thereceiver can sample 10 etus synchronously (including the START-BIT, theDATA BYTE, i.e. one byte of the transmitted data, and the STOP-BIT).

Once the receiver has extracted one sample per etu from the digitalizedenvelope, it can recover the transmitted bits (i.e. control data (suchas the bits of SOF-LOW etc.) as well as the transmitted data of the DATABYTE) using a processing as illustrated in FIG. 8.

FIG. 8 shows the architecture of a data recovery module 800 according toan embodiment.

The data recovery module 800 includes a comparator 802 which generatesthe current data bit b[i] (i.e. the ith recovered data bit) by comparingthe current sample x[i] (of the digitalized envelope after LPF, if any,of an etu of a DATA BYTE) with a current threshold thr[i].

The data recovery module 800 derives the threshold from a look-up table803 containing sample values data_(xy0) and data_(xy1) which occurredwhen a zero and a one have been received, respectively, after havingfirst received a certain combination xy of the preceding two bits. Forthe current bit b[i], the preceding two bits are {b[i−2], b[i−1]}. Ifb[i−2]=x and b[i−1]=y, an adder 804 and a divider 805 set the thresholdto detect the current bit to (data_(xy0)+data_(xy1))/2.

For each data bit b[i], the corresponding table entry (depending onb[i−2], b[i−1]) is updated with the sample x[i]. For the indexing of thetable 803, the past (or preceding) bits b[i−2], b[i−1] are stored by a2-bit shift register 806 and the current bit b[i] is fed back via afeedback path 807. The current recovered bit is held by a register 801which is updated with the bit rate frequency f_(bit).

The size of the table 803 (i.e. the number of previous bits considered)is chosen considering the ISI in the input signal. The 8-entry table asillustrated in FIG. 8 is sufficient to support the current ISO14443requirements (ASK up to 6.8 Mbit/s).

According to various embodiments, in order to start the reception, thelook-up table 803 is initialized (trained) by exploiting the informationavailable in the SOF (unless a training sequence is available accordingto the advanced frame option: in this case the table initialization isstraightforward).

After initialization, the table 803 can be updated dynamically at eachreceived bit thus allowing the receiver to follow drifts in theenvelope.

FIG. 9 illustrates the training procedure for an input signal 910 equalto the input signal 710.

(1) On the first edge, the complete table 803 is loaded with a MAX value(e.g. an 8 step older sample of the digitalized envelope x[i−8] derivedfrom a FIFO where the samples are stored).

(2) On the first received bit, the table entries corresponding to thebit sequences xy0 are loaded with the sampled data (110).

(3) Table entries for 100 and 000 are updated during the reception ofSOF-low.

(4) On the last zero of SOF-low, the table entries for 001 and 011 areloaded with the current sample (000) to ensure the correct reception ofthe SOF-high.

(5) On the first bit after the rising edge of SOF-high, the table valuesfor 001 and 101 are updated with the current sample (001).

(6) On the second bit after the rising edge of SOF-high, the table entryfor 011 is updated.

This initialization gives rise to threshold values thr[i] 901.

FIG. 10 shows an ASK receiver 1000 based on the synchronisationdescribed with reference to FIG. 5 and the data recovery described withreference to FIG. 6.

The receiver 1000 includes a track&hold circuit 1001, e.g. correspondingto the peak detector 208, an ADC 1002, e.g. corresponding to the ADC209, a low-pass filter 1003, e.g. corresponding to the low pass filter501, a slew rate limiter 1004, e.g. corresponding to slew rate limiter502, a differentiator 1005, e.g. corresponding to differentiator 503, abuffer 1006, a threshold determination module 1007, e.g. correspondingto table 803, adder 804 and divider 805, a comparator 1008, e.g.corresponding to comparator 802, a 2-bit shift register 1009, e.g.corresponding to shift register 806, a finite state machine 1010, an8-bit shift register 1011 and a controller 1012.

The ADC 1002 and the low-pass filter 1003 are part of a first clockdomain 1013 with a clock frequency of f_(ADC), the slew rate limiter1004, the differentiator 1005 and the buffer 1006 are part of a secondclock domain 1014 with clock frequency f_(SAMPLE) and the thresholddetermination module 1007, the comparator 1008, the 2-bit shift register1009, the finite state machine 1010, the 8-bit shift register 1011 andthe controller 1012 are part of a third clock domain 1015 with clockfrequency fbit, wherein f_(bit)=B_(r), f_(SAMPLE)=8×f_(bit) and f_(ADC)is the ADC conversion frequency and fADC≥fSAMPLE. It should be notedthat in general, a different number of samples per etu could be used.

The finite state machine 1010 has states corresponding to the positionswithin the received signal (e.g. within SOF-low, within DATA BYTE etc.)and outputs corresponding signals to the controller 1012 which controlsthe other components of the receiver accordingly, e.g. switches on thesynchronizer, routes the transmitted data to other components (i.e.separates the recovered control data from the recovered useful data)etc. For example, the controller 1012 controls the 8-bit shift register1011 to receive and store a byte of recovered (useful) data to beforwarded to another component for further processing.

The slew rate limiter 1004 may be implemented as filter directly basedon equation (1).

FIG. 11 shows a differentiator 1100 as an example of an implementationof the differentiator 1005.

In this example, n_(diff)=6.

The differentiator includes a chain of registers 1101 to 1108 which eachstore an output sample of the slew rate limiter 1004 and which areclocked with f_(SAMPLE), i.e. the samples propagate with f_(SAMPLE) fromleft to right to the chain of registers 1101 to 1108. The chain ofregisters 1101 to 1108 thus can be seen to form an 8-value FIFO (firstin first out) register.

The current output sample of the slew rate limiter 1004 is supplied tolast two registers 1107, 1108 of the 8-value FIFO. The sample stored inthe sixth register 1106 is supplied to an inverter 1110. The output ofthe buffer 1109 and the output of the inverter 1110 are added by anadder 1111 and a comparator 1112 compares the result with the thresholdthr_(diff) and, depending on whether a rising or a falling edge is to bedetected, as indicated by a signal dir, outputs a sync pulse if theresult is above the threshold thr_(diff) or below the thresholdthr_(diff), respectively.

At the beginning of the reception (SOF falling edge), y[i−8]==x[i−8]==MAX is the value used to load the training table according to (1) asdescribed above, e.g. provided by the differentiator 1100 via the buffer1006.

In summary, according to various embodiments, a communication device isprovided as illustrated in FIG. 12.

FIG. 12 shows a communication device 1200.

The communication device 1200 includes a sampler 1201 configured tosample an input signal, wherein the sampler 1201 is configured togenerate a sampled value for each sampling time of a sequence ofsampling times.

Further, the communication device 1200 includes a sequence valuegenerator 1202 configured to generate an output value for each samplingtime of the sequence of sampling times based on the sampled values,wherein the sequence value generator 1202 is configured to set theoutput value for a sampling time based on the sampled value for thesampling time and based on a limitation of the difference between theoutput value for the sampling time and the output value for thepreceding sampling time in the sequence of sampling times.

The communication device 1200 further includes an edge detector 1203configured to detect an edge in the input signal based on the outputvalues.

According to one embodiment, in other words, the slew rate of an inputsignal at an edge (rising edge or falling edge) is limited by processingthe sample values before edge detection. For example, for each sampleinterval, the amount that the (processed) sample values may change (i.e.the change over one sample interval, i.e. from one sample value to thenext) is limited, e.g. to a maximum value if it exceeds a threshold(e.g. the maximum value to which it is capped). The resulting processedsampled values (denoted as output values of the sequence valuegenerator, e.g. slew rate delimiter) are then used for edge detection.The limitation of the difference may for example be set such that theoutput values (or the slew of the output values) are independent fromthe modulation index, e.g. in context of ASK (amplitude shift keying).For example, it may be set such that the slew is limited to a slew whichoccurs when using a minimal modulation index (of, e.g., a plurality ofavailable modulation indexes).

The communication device 1200 for example carries out a method asillustrated in FIG. 13.

FIG. 13 shows a flow diagram 1300 illustrating a method for detecting anedge in a received signal.

In 1301, an input signal is sampled including generating a sampled valuefor each sampling time of a sequence of sampling times.

In 1302, an output value is generated for each sampling time of thesequence of sampling times based on the sampled values, includingsetting the output value for a sampling time based on the sampled valuefor the sampling time and based on a limitation of the differencebetween the output value for the sampling time and the output value forthe preceding sampling time in the sequence of sampling times.

In 1303, an edge in the input signal is detected based on the outputvalues.

Further, according to various embodiments, a communication device isprovided as illustrated in FIG. 14.

FIG. 14 shows a communication device 1400.

The communication device 1400 includes a receiver 1401 configured toreceive a signal representing a predefined sequence of digital valuesfrom a transmitter and a sampler 1402 configured to sample the signalfor each digital value of the predefined sequence of digital values

Further, the communication device 1400 includes a memory 1403 configuredto store a table giving, for each of a plurality of combinations of oneor more preceding first digital values and a following second digitalvalue, a threshold for a signal level to detect the second digitalvalue, wherein the predefined sequence of digital values represented bythe received signal includes a subset of the plurality of combinations.

The communication device 1400 further includes an initializer 1404configured to for a combination in the subset of the plurality ofcombinations, initialize the table based on a sample of the signal forthe second value and for a combination outside of the subset, select acombination from the subset and initialize the table based on a sampleof the signal for the second value of the selected combination.

Further, the communication device 1400 includes a data recovery circuit1405 configured to receive data from the transmitter based on theinitialized table.

According to one embodiment, in other words, a predefined sequence whichis not a complete training sequence, i.e. which lacks possiblecombinations of successive digital values (e.g. bit values), e.g. doesnot contain all possible combinations of a certain length is used toinitialize a table indicating detection thresholds for combinations(e.g. all possible value combinations) of the length. In other words, asample value of a combination is used to initialize the table for adifferent combination.

The predefined sequence is for example a synchronization sequence. Forexample, the communication device and the transmitter communicate (sendand receive) signals according to a radio frame structure, e.g.according to a radio communication protocol (e.g. a contactless chipcard communication protocol such as ISO 14443) and the synchronizationsequence is a sequence indicating the start of a frame according to theradio frame structure.

The communication device 1400 for example carries out a method asillustrated in FIG. 15.

FIG. 15 shows a flow diagram 1500 illustrating a method for receivingdata.

In 1501, a signal is received from a transmitter representing apredefined sequence of digital values from a transmitter.

In 1502, the signal is sampled for each digital value of the predefinedsequence of digital values.

In 1503, a table is initialized giving, for each of a plurality ofcombinations of one or more preceding first digital values and afollowing second digital value, a threshold for a signal level to detectthe second digital value, wherein the predefined sequence of digitalvalues represented by the received signal includes a subset of theplurality of combinations. The initializing includes for a combinationin the subset of the plurality of combinations, initializing the tablebased on a sample of the signal for the second value, and for acombination outside of the subset, selecting a combination from thesubset and initializing the table based on a sample of the signal forthe second value of the selected combination.

In 1504, data are received data from the transmitter based on theinitialized table.

In the following, various embodiments are given.

Embodiment 1 is a communication device as illustrated in FIG. 12.

Embodiment 2 is the communication device of embodiment 1, wherein thesequence value generator is configured to set the output value for eachsampling time of the sequence of sampling times except the firstsampling time of the sequence of sampling times based on the sampledvalue for the sampling time and based on a limitation of the differencebetween the value for the sampling time and the value for the precedingsampling time in the sequence of sampling times.

Embodiment 3 is the communication device of embodiments 1 or 2, whereinthe sequence value generator is configured to set the output value forthe first sampling time of the sequence of sampling times based on thesampling value of the first sampling time of the sequence of samplingtimes.

Embodiment 4 is the communication device of embodiments 1 or 2, whereinthe sequence value generator is configured to set the output value forthe first sampling time of the sequence of sampling times equal to thesampling value of the first sampling time of the sequence of samplingtimes.

Embodiment 5 is the communication device of any one of embodiments 1 to4, wherein the edge detector is configured to detect an edge based onwhether the difference between the output value for the first samplingtime on the output value for a later sampling time is below apredetermined threshold.

Embodiment 6 is the communication device of any one of embodiments 1 to5, wherein the sequence value generator is configured to set the outputvalue for a sampling time based on the sampled value for the samplingtime and based on a limitation of the difference between the outputvalue for the sampling time and the output value for the precedingsampling time in the sequence of sampling times to a fixed value.

Embodiment 7 is the communication device of embodiment 6, wherein theedge detector is configured to detect an edge at a candidate samplingtime of the sequence of sampling times based on whether the output valuehas fallen from each sampling time to the next sampling time between thefirst sampling time and the candidate sampling time.

Embodiment 8 is the communication device of any one of embodiments 1 to7, wherein the sequence value generator is configured to check whetherthe difference between a sampled value for a sampling time and theoutput value for the preceding sampling time in the sequence of samplingtimes is above a predetermined threshold and, if the difference is abovethe predetermined threshold, generate an output value for the samplingtime to limit the difference to or below the predetermined threshold.

Embodiment 9 is the communication device of embodiment 8, wherein thesequence value generator is configured to, if the difference is abovethe predetermined threshold, set the output value to the sampled valueof the preceding sampling time minus a predetermined value if thedifference is negative or plus a predetermined value if the differenceis positive.

Embodiment 10 is the communication device of embodiment 9, wherein thepredetermined value is the predetermined threshold.

Embodiment 11 is the communication device of any one of embodiments 1 to10, wherein the edge detector is configured to detect a rising edgebased on whether the output values increase over the sequence ofsampling times.

Embodiment 12 is the communication device of any one of embodiments 1 to11, wherein the edge detector is configured to detect a falling edgebased on whether the output values decrease over the sequence ofsampling times.

Embodiment 13 is the communication device of any one of embodiments 1 to12, wherein the input signal is modulated based on amplitude shiftkeying.

Embodiment 14 is a method for detecting an edge in a received signal asillustrated in FIG. 13.

Embodiment 15 is a communication device as illustrated in FIG. 14.

Embodiment 16 is the communication device of embodiment 15, wherein theinitializer is configured to select the combination from the subsetaccording to a predetermined selection criterion.

Embodiment 17 is the communication device of embodiment 15 or 16,wherein the initializer is configured to select the combination from thesubset based on that at least one of the first digital values of theselected combination is equal to the corresponding first digital valueof the combination outside of the subset.

Embodiment 18 is the communication device of any one of embodiments 15to 17, wherein the initializer is configured to select the combinationfrom the subset based on that the second digital value of the selectedcombination is equal to the second digital value of the combinationoutside of the subset.

Embodiment 19 is the communication device of any one of embodiments 15to 18, wherein the signal is based on a transmission of the predefinedsequence of digital values by the transmitter.

Embodiment 20 is the communication device of any one of embodiments 15to 19, wherein the signal is modulated based on the predefined sequenceof digital values.

Embodiment 21 is the communication device of any one of embodiments 15to 20, wherein the signal is modulated based on amplitude shift keying.

Embodiment 22 is the communication device of any one of embodiments 15to 21, wherein each combination includes two preceding first digitalvalues and one following second digital value.

Embodiment 23 is the communication device of any one of embodiments 15to 22, wherein the plurality of combinations includes all possiblecombinations of values for the preceding first values and the followingsecond value.

Embodiment 24 is the communication device of any one of embodiments 15to 23, wherein the first digital values and the second digital valuesare bit values.

Embodiment 25 is the communication device of any one of embodiments 15to 24, further including an updater configured to at least one of for acombination in the subset of the plurality of combinations, update theinitialized table based on a sample of the signal for the second value;and for a combination outside of the subset, select a combination fromthe subset and update the initialized table based on a sample of thesignal for the second value of the selected combination.

Embodiment 26 is a method for receiving data as illustrated in FIG. 15.

According to a further embodiment, a communication device is providedincluding a slew rate limiter configured to limit the slew in a sequenceof sample values of an input signal and an edge detector configured todetect an edge in the input signal based on the slew-rate limitedsequence of sample values.

According to a further embodiment, a communication device is providedhaving a table which stores data detection thresholds for a set ofdifferent combinations of preceding sample values and an initializerconfigured to initialize the table based on the received signal valuesfor a (proper) subset of the set of combinations.

It should be noted that embodiments described in context of one of thecommunication devices are analogously valid for the other communicationdevices and the methods and vice versa and embodiments may be combinedwith each other. In particular, a communication device according to bothFIGS. 12 and 14 may be provided.

The communication devices may for example be implemented by chip cardmodules, including devices such as RFID (radio-frequency identification)transponders.

One or more or a combination of the embodiments as described above mayfor example be used to implement an ASK synchronous receiver whichsupports ISO14443 type-B frames without synchronization and trainingpatterns.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

What is claimed is:
 1. A communication device, comprising: a receiverconfigured to receive a signal representing a predefined sequence ofdigital values from a transmitter; a sampler configured to sample thesignal for each digital value of the predefined sequence of digitalvalues; a memory configured to store a table giving, for each of aplurality of combinations of one or more preceding first digital valuesand a following second digital value, a threshold for a signal level todetect the second digital value, wherein the predefined sequence ofdigital values represented by the received signal includes a subset ofthe plurality of combinations; an initializer configured to, for acombination in the subset of the plurality of combinations, initializethe table based on a sample of the signal for the second value; and fora combination outside of the subset, select a combination from thesubset and initialize the table based on a sample of the signal for thesecond value of the selected combination; and a data recovery circuitconfigured to receive data from the transmitter based on the initializedtable.
 2. The communication device of claim 1, wherein the initializeris configured to select the combination from the subset according to apredetermined selection criterion.
 3. The communication device of claim1, wherein the initializer is configured to select the combination fromthe subset based on whether at least one of the first digital values ofthe selected combination is equal to the corresponding first digitalvalue of the combination outside of the subset.
 4. The communicationdevice of claim 1, wherein the initializer is configured to select thecombination from the subset based on whether the second digital value ofthe selected combination is equal to the second digital value of thecombination outside of the subset.
 5. The communication device of claim1, wherein the signal is based on a transmission of the predefinedsequence of digital values by the transmitter.
 6. The communicationdevice of claim 1, wherein the signal is modulated based on thepredefined sequence of digital values.
 7. The communication device ofclaim 1, wherein the signal is modulated based on amplitude shiftkeying.
 8. The communication device of claim 1, wherein each combinationincludes two preceding first digital values and one following seconddigital value.
 9. The communication device of claim 1, wherein theplurality of combinations includes all possible combinations of valuesfor the preceding first values and the following second value.
 10. Thecommunication device of claim 1, wherein the first digital values andthe second digital values are bit values.
 11. The communication deviceof claim 1, further comprising: an updater configured to at least one offor a combination in the subset of the plurality of combinations, updatethe initialized table based on a sample of the signal for the secondvalue; and for a combination outside of the subset, select a combinationfrom the subset and update the initialized table based on a sample ofthe signal for the second value of the selected combination.
 12. Amethod for receiving data, the method comprising: receiving a signalrepresenting a predefined sequence of digital values from a transmitter;sampling the signal for each digital value of the predefined sequence ofdigital values; initializing a table giving, for each of a plurality ofcombinations of one or more preceding first digital values and afollowing second digital value, a threshold for a signal level to detectthe second digital value, wherein the predefined sequence of digitalvalues represented by the received signal includes a subset of theplurality of combinations, wherein the initializing comprises for acombination in the subset of the plurality of combinations, initializingthe table based on a sample of the signal for the second value; and fora combination outside of the subset, selecting a combination from thesubset and initializing the table based on a sample of the signal forthe second value of the selected combination; and receiving data fromthe transmitter based on the initialized table.
 13. The method of claim12, wherein selecting the combination from the subset comprisesselecting the combination from the subset according to a predeterminedselection criterion.
 14. The method of claim 12, wherein selecting thecombination from the subset is based on whether at least one of thefirst digital values of the selected combination is equal to thecorresponding first digital value of the combination outside of thesubset.
 15. The method of claim 12, wherein selecting the combinationfrom the subset is based on whether the second digital value of theselected combination is equal to the second digital value of thecombination outside of the subset.
 16. The method of claim 12, whereinthe signal is based on a transmission of the predefined sequence ofdigital values by the transmitter.
 17. The method of claim 12, whereinthe signal is modulated based on the predefined sequence of digitalvalues.
 18. The method of claim 12, wherein the signal is modulatedbased on amplitude shift keying.
 19. The method of claim 12, whereineach combination includes two preceding first digital values and onefollowing second digital value.
 20. The method of claim 12, wherein theplurality of combinations includes all possible combinations of valuesfor the preceding first values and the following second value.